Axial piston pump or motor



Sept. 27, 1966 o. H. THOMA 3,274,949

AXIAL PISTON PUMP on MOTOR Filed Aug. 10, 1964 2 Sheets-Sheet l INvENTQR 0514mm 7390/14/ 1 ATTORNEY Sept. 27, 1966 o. H. THOMA AXIAL PISTON PUMP OR MOTOR 2 Sheets-sheet 2 Filed Aug. 10,. 1964 INVENTOR flaw/2L0 WW A'T TORN EY United States Patent Office 3,274,94fl Patented Sept. 27, 1966 3,274,949 AXIAL PISTON PUMP R MOTOR Oswald H. Thoma, Cheltenham, England, assignor to Hydraulic-Drive A.G., Glarus, Switzerland, a Swiss company Filed Aug. 10, 1964, Ser. No. 388,529 6 Claims. (Cl. 103162) This invention relates to an axial piston fluid displacement machine such as a pump or motor, having a rotary cylinder block and a connecting shaft, the block being formed with a number of parallel cylinder bores whose pistons slide on a non-rotating slanting disc. Such machines usually have a valve body formed with inlet and outlet control openings to co-operate with ports formed in the adjacent end surface of the cylinder block and communicating respectively with the cylinder bores. This type of machine can be used as a pump or motor or selectively as a motor/pump, and its fluid displacement relative to its maximum capacity can be varied, if need be, by adjustment or replacement of the slanting disc. Hitherto small capacity machines of this type have been disproportionately expensive, since the cost, for example the number of different components required is essentially the same, irrespective of the capacity, so that for a small performance, such pumps and motors are relatively expensive.

An object of the invention is to provide a simpler and more economical machine of this type, especially for smaller performances.

The invention consists broadly in an axial piston fluid displacement pump or motor comprising a rotary cylinder block, and a connecting shaft, the block having three equally spaced parallel cylinder bores whose pistons engage a non-rotating slanting disc, and a stationary valve body against which one surface of the cylinder block bears and which is formed with inlet and outlet control openings to co-operate with ports in the cylinder block communicating with each cylinder bore, the centres of the ports being displaced radially outwards from the centres of the bores in the cylinder block, thus affording an increased central area for attachment of the shaft.

Preferably the major part of the cross-sectional area of each port lies outside the pitch circle on which the centres of the bores in the cylinder block lie.

The ports may be elongated circumferentially.

A noticeably lower price per machine is achieved through the small number of cylinder bores and the corresponding small number of pistons and other components. The positioning of the ports greatly facilitates the attachment of the shaft to the cylinder block, since with a small number of cylinder bores it is desirable that each bore should be of substantial diameter, and thus there is relatively little material of the 'block available adjacent the axis to provide for attachment of the shaft.

According to a preferred feature of the invention a flexible coupling is arranged between the shaft and the cylinder block.

The cylinder block may be supported by a' bearing surrounding the block at an axial position adjacent the pistons.

This preferred construction permits the cylinder block to align itself accurately with the stationary surface of the valve body, without materially affecting or being affected by the shaft.

The invention may be performed in various ways, and two specific embodiments will now be described by way of example with reference to the accompanying drawings in which,

FIGURE 1 is a sectional elevation through an axial piston hydraulic motor, according to the invention,

FIGURE 2 is an end view of the cylinder block of the motor of FIGURE 1,

FIGURE 3 is a sectional elevation through a modified form of hydraulic pump according to the invention, and

FIGURE 4 is an end view of the cylinder :block of FIGURE 3.

Referring firstly to FIGURES 1 and 2, the casing of the hydraulic motor comprises a cylindrical-shaped wall part 1 having an integral end piece, and a removable end cover 2. Within the casing a cylinder block 3 is mounted for rotation about the axis of the casing. The cylinder block is formed with three cylinder bores 5 positioned parallel to the rotary axis and equally spaced apart about the axis of the cylinder block, see FIGURE 2. In each cylinder bore 5 a piston 6 is mounted for endwise sliding movement. Each piston 6 is pivotally connected to a sliding shoe 7 which engages a slanting disc 8 which is firmly fixed by a pin 9 in the casing 1. The cylinder block rotates with its front surface 10, i.e., the surface remote from the slanting disc 8, against the inner surface 11 of the end cover 2 which also constitutes a valve body. In the inner surface 11. of the end cover are provided two kidney-shaped valve ports or control openings 12, 13 communicating with fluid channels 14, 15. One of the channels serves as inlet, and the other as an outlet, for the pressure fluid. In the cylinder block 3 a port 16 leads from each cylinder bore 5 to the front surface 10 of the block and as the block rotates each port thus communicates in sequence with the inlet and outlet control openings 12, 13. A spring 17 is fitted in each cylinder bore and acts to urge the respective shoe 7 against the slanting disc 8, and also urges the cylinder block 3 against the inner surface 11 of the cover 2.

A shaft 13 is attached to the front surface 10 of the cylinder block 3 by means of a central threaded bolt 19 and one or more pins 20. Alternatively the shaft can be for-med integral with the cylinder block. In order to allow the shaft 20 and its connection with the cylinder block to be of the necessary strength the ports 16 are positioned at points displaced radially outwards from the centres of the bores 5. As seen in FIGURE 2 the circle 21 on which the centres of the ports lie has a larger diameter than the circle 22 on which the centres of the cylinder bores 5 lie. It will be understood that the ports 16 may be inclined radially outwards if desired.

It will also be noted that the external diameter of the shaft 18 and particularly the diameter of the flange 18A on the shaft which engages the end face 10 of the cylinder block is appreciably greater than the pitch circle diameter D of the radially innermost parts of the bores 5.

A hearing 4 is arranged at an axial position corresponding to the centre of the effective stroke of the pistons 6 and supports the block 3 against lateral loads. As this construction cannot withstand any considerable side force on the shaft it would be expedient to provide, between the block 3 and the shaft 18 a flexible coupling, i.e., an Oldham coupling.

The pump illustrated in FIGURES 3 and 4 is in main essentials identical with that illustrated in FIGURES 1 and 2, and corresponding parts are indicated by the same reference numerals, with an added sufiix.

In this example the ports 16 are elongated circumferentially as seen in FIGURE 4, and extend substantially across the full width of the respective bore 5, the major part of the area of each port being radially outside the pitch circle 22 on which lie the centres of the bores 5'. In this construction the end face of the cylinder block does not make contact with the whole of the inner face 11' of the valve body or end cover 2', but only with a limited area provided by an annular band 25, in which 3 are provided the kidney-shaped control openings 12', and 13.

The shaft 18' is not connected directly to the cylinder block, but is mounted in bearings 26 supported in a housing 27 fixed to the end cover 2'. A stub shaft 28 is firmly attached to the end face of the cylinder block by means of a screw threaded bolt 19' and a pin 20', and a flexible coupling is provided between the shaft 18 and stub shaft 28 in the form of a splined sleeve 29, engaging corresponding splines on the parts 18' and 28. This permits limited angular displacement between the shaft 18 and the cylinder block, and allows the block to align itself with the face of the end cover, without being affected by angular displacement of the shaft axis.

It will also be noted that the external diameter of the stub shaft 28 where it engages the front surface of the cylinder block 3 is considerably greater than the pitch circle diameter D of the radially innermost parts of the bores What is claimed is:

1. An axial piston fluid displacement pump or motor comprising a rotary cylinder block, a connecting shaft secured to said block at one end thereof, said block having three equally spaced parallel cylnder bores closely adjacent to the rotary axis of the cylinder block, such that the pitch circle diameter of the radially innermost parts of the bores is substantially less than the diameter of the connecting shaft where it engages the block, a non-rotary slanting cam disc at the end of said block remote from said connecting shaft, pistons slidable in said bores and engaging said cam disc, a stationary ported valve body at the same end of said block as said connecting shaft, said valve body having an axially directed surface, against which one end surface of the cylinder block bears, and said axially directed surface of the valve body being formed with inlet and outlet control openings to cooperate with ports in said end surface of the cylinder block communicating with each cylinder bore, the cen ter of the ports being displaced radially outwards from the respective centers of the bores in the cylinder block, thus affording an increased central area for attachment of the shaft.

2. An axial piston pump or motor according to claim 1, in which the major part of the cross-sectional area of each port lies outside the pitch circle on which the centres of the bores in the cylinder block lie.

3. An axial piston pump or motor according to claim 2, in which the ports are elongated circumferentially.

4. An axial piston pump or motor according to claim 1, in which the cylinder block is supported 'by a bearing surrounding the block at an axial position adjacent the pistons.

5. An axial piston pump or motor according to claim 1, including a flexible coupling connected to the connecting shaft adjacent said cylinder block.

6. An axial piston pump or motor according to claim 5, including a bearing supporting the shaft from the casing of the machine.

References Cited by the Examiner UNITED STATES PATENTS 1,678,556 7/1928 Copson 103-l62 2,525,498 10/1950 Naylor et al l03-162 2,543,624 2/1951 Gabriel l03162 2,608,159 8/1952 Born 103--l62 MARTIN P. SCHWADRON, Primary Examiner.

SAMUEL LEVINE, Examiner.

R. M. VARGO, Assistant Examiner. 

1. AN AXIAL PISTON FLUID DISPLACEMENT PUMP OR MOTOR COMPRISING A ROTARY CYLINDER BLOCK, A CONNECTING SHAFT SECURED TO SAID BLOCK AT ONE END THEREOF, SAID BLOCK HAVING THREE EQUALLY SPACED PARALLEL CYLINDER BORES CLOSELY ADJACENT TO THE ROTARY AXIS OF THE CYLINDER BLOCK, SUCH THAT THE PITCH CIRCLE DIAMETER OF THE RADIALLY INNERMOST PARTS OF THE BORES IN SUBSTANTIALLY LESS THAN THE DIAMETER OF THE CONNECTING SHAFT WHERE IT ENGAGES THE BLOCK, A NON-ROTARY SLANTING CAM DISC AT THE END OF SAID BLOCK REMOTE FROM SAID CONNECTING SHAFT, PISTONS SLIDABLE IN SAID BORES AND ENGAGING SAID CAM DISC, A STATIONARY PORTED VALVE BODY AT THE SAME END OF SAID BLOCK AS SAID CONNECTING SHAFT, SAID VALVE BODY HAVING AN AXIALLY DIRECTED SURFACE, AGAINST WHICH ONE END SURFACE OF THE CYLINDER BLOCK BERS, AND SAID AXIALLY DIRECTED SURFACE OF THE VALVE BODY BEING FORMED WITH INLET AND OUTLET CONTROL OPENINGS TO COOPERATE WITH PORTS IN SAID END SURFACE OF THE CYLINDER BLOCK COMMUNICATING WITH EACH CYLINDER BORE, THE CENTER OF THE PORTS BEING DISPLACED RADIALLY OUTWARDS FROM THE RESPECTIVE CENTERS OF THE BORES IN THE CYLINDER BLOCK, THUS AFFORDING AN INCREASED CENTRAL AREA OF ATTACHMENT OF THE SHAFT. 